Method and apparatus for chroma reconstruction

Abstract

A method and apparatus for predicting chroma values including the steps of having a decoder provide an image frame to an up-sample filter, the image frame having luma and chroma components, and applying an analysing algorithm on a subset of said image frame to obtain the subset content type, and, depending on the content type, select a reconstruction algorithm to reconstruct the chroma components.

The invention claimed is: 
     
       1. A method for predicting chroma values using a decoder, and an up-sample filter, comprising the steps of:
 having the decoder provide an image frame to the up-sample filter, said image frame comprising luma and chroma components, 
 having the up-sampling filter define a subset of said image frame, and applying at least one analysing algorithm on said subset to obtain a subset content type, and 
 selecting at least one reconstruction algorithm to reconstruct the chroma components of the subset wherein the selecting of the at least one reconstruction algorithm depends on the subset content type, and wherein a size of the subset is at least 2 by 2 pixels in full chroma resolution, 
 wherein the at least one analysing algorithm comprises the step of investigating if the chroma subset has the same or substantially the same structure, or the same or substantially the inverse structure, of the luma subset. 
 
     
     
       2. A method according to  claim 1 , wherein the decoder is a hardware accelerated decoder. 
     
     
       3. A method according to  claim 1 , wherein the chroma components are reconstructed with the values of the luma components. 
     
     
       4. A method according to  claim 1 , wherein an analysing algorithm comprises the step of investigating if at least two luma components in the subset have the same value. 
     
     
       5. A method according to  claim 1 , wherein the reconstruction algorithm comprises the steps of implementing formulas of an up-sampling algorithm wherein, and for neighboring luma components being equal, arranging the corresponding chroma components to be equal. 
     
     
       6. A method according to  claim 1 , wherein a reconstruction algorithm comprises the steps of,
 normalizing the full-resolution luma component with a minimum and maximum sub-sampled luma component, 
 and linearly scaling it to the sub-sampled chroma component. 
 
     
     
       7. A method according to  claim 1 , wherein a position of the subset is repeatedly moved so that eventually the whole image frame is analysed and reconstructed. 
     
     
       8. An apparatus for predicting chroma values, comprising:
 a decoder arranged to receive and provide an image frame, said image frame comprising luma and chroma components, and 
 an up-sampling unit, comprising an up-sampling filter performing reconstruction, arranged to receive image frames from the decoder and defining at least one subset of each image frame, wherein for each subset of the image frame, said up-sampling unit is configured to select at least one reconstruction algorithm to reconstruct the chroma components of the subset so that the selected reconstruction algorithm depends on a content type of the subset, 
 wherein a size of the subset is at least 2 by 2 pixels in full chroma resolution, 
 further comprising analysing algorithm means adapted to investigate if the chroma subset has the same or substantially the same structure, or the inverse structure or substantially the inverse structure, of the luma subset. 
 
     
     
       9. The apparatus according to  claim 8 , wherein the decoder is a hardware accelerated decoder. 
     
     
       10. The apparatus according to  claim 8 , a wherein the upsampling unit is adapted to reconstruct the chroma components with the values of the luma components. 
     
     
       11. The apparatus according to  claim 8 , further comprising analysing algorithm means adapted to investigate if at least two luma components in the subset have the same value. 
     
     
       12. The apparatus according to  claim 8 , wherein the reconstruction algorithm is adapted to implement the formulas of an up-sampling algorithm wherein, for neighbouring luma components being equal, the corresponding chroma components are arranged to be equal. 
     
     
       13. The apparatus according to  claim 8 , wherein the up-sampling filter for performing reconstruction is adapted to normalize the full-resolution luma component with the minimum and maximum sub-sampled luma component, and linearly to scale it to the sub-sampled chroma component. 
     
     
       14. The apparatus according to  claim 8 , wherein the apparatus is further adapted so that the above-mentioned subset can be placed in a multiple of positions, said multiple of positions being located so that eventually the whole frame can be analysed and reconstructed. 
     
     
       15. A computer program product comprising a non-transitory machine-readable medium carrying instructions which, when executed by a processor, cause the processor to perform the method of  claim 1 . 
     
     
       16. The method according to  claim 1 , wherein the subset content type is identified as natural screen content or synthetic screen content. 
     
     
       17. A method for predicting chroma values using a decoder, and an up-sample filter, comprising the steps of:
 having the decoder provide an image frame to the up-sample filter, said image frame comprising luma and chroma components, 
 having the up-sampling filter define a subset of said image frame, and applying at least one analysing algorithm on said subset to obtain a subset content type, and 
 selecting at least one reconstruction algorithm to reconstruct the chroma components of the subset wherein the selecting of the at least one reconstruction algorithm depends on the subset content type, and wherein a size of the subset is at least 2 by 2 pixels in full chroma resolution, 
 wherein the reconstruction algorithm comprises the steps of: 
 implementing formulas of an up-sampling algorithm wherein, and for neighboring luma components being equal, arranging the corresponding chroma components to be equal, or 
 normalizing the full-resolution luma component with a minimum and maximum sub-sampled luma component, and linearly scaling it to the sub-sampled chroma component. 
 
     
     
       18. The method according to  claim 17 , wherein the decoder is a hardware accelerated decoder. 
     
     
       19. The method according to  claim 17 , wherein the chroma components are reconstructed with the values of the luma components. 
     
     
       20. The method according to  claim 17 , wherein an analysing algorithm comprises the step of investigating if at least two luma components in the subset have the same value.